Auto-oxidation of alkylated anthraquinones



United States Patent O AUTO-OXIDATION F ALKYLATED ANTHRAQUINONES Lynn H. Dawsey, Robert R. Umhoefer, and Carl K.

Muehlhausser, Kenmore, N. Y., assignors, by mesne assignments, to Food Machinery and Chemical Corporation, San Jose, Calif., a corporation of Delaware No Drawing. Application December 14, 1951, Serial No. 261,762

6 Claims. (Cl. 23-207) The present invention relates to the production of hydrogen peroxide by cyclic hydrogenation and oxidation in an improved solvent medium of alkylated anthraquinones or tetrahydroalkylated anthraquinones.

It has been proposed to produce hydrogen peroxide from hydrogen and oxygen gases through alternate oxidation reduction of alkylated anthraquinones dissolved in organic solution. The production of the hydrogen peroxide by this process proceeded in two main stages: (1) the hydrogenation stage where the alkylated quinone was reduced to the alkylated hydroquinone and (2) the oxidation stage where the alkylated hydroquinone was oxidized to the quinone, hydrogen peroxide splitting oif during this operation. After separation of the hydrogen peroxide and the purification of the solution, the cycle of the two stages was repeated. This type of procedure has been described in U. S. Patents 2,158,525 and 2,215,833 and its commercial application in PB Report 395.

In this prior method of manufacture, a mixed solvent was suggested as the reaction medium consisting of a constituent capable of dissolving the quinone material and a constituent capable of dissolving the hydroquinone material. The practical result achieved was that the solution could be ultimately oxidized and reduced in cyclic fashion in the liquid phase without separation of either form of the working material. The quinone solvent normally employed has been an ether, 2. hydrocarbon (usually benzene) or similar solvent of high vapor pressure and therefore inflammable. Such hydrocarbons have practically zero dissolving power for the hydroquinone form of the working compound, but excellent dissolving power for the quinone form. The hydroquinone solvent component has consisted of the higher aliphatic alcohols. However, the solubility of the hydroquinones in the higher alcohols is not very great and this limits the amount of hydroquinone that can be treated or worked per cycle which, in turn, limits the amount of hydrogen peroxide that can be produced per cycle. General experience in operation of the prior process, as outlined in the literature cited above, indicates that about 40% of dissolved compound may be successfully worked With the realization of hydrogen peroxide concentrations of about 5.5 grams per liter in the organic solution, after the oxidation phase of the cycle.

In producing hydrogen peroxide from the hydroqui nones and particularly the alkylated hydroquinones or the corresponding tetrahydro alkylated hydroquinones, it has been necessary heretofore to utilize relatively pure oxygen and it has been necessary to carry out the oxidation in closed systems to prevent excessive loss of solvent. It has not been possible to use free air to render the mixture less liable to explosion and fire hazard by reason of volatility of the generally employed solvents, such asbenzene, anisole, combustible alcohols and the like. Although the preparation of hydrogen peroxide by auto-oxidation processes appears to be economically favorable when carried out upon a limited scale, the operational hazards presented by the explosive vapors and the disadvantage connected with oxidation in a closed system with oxygen on a large scale renders the whole process impractical.

Contrasted with the German practice of using an alcohol in combination with a hydrocarbon as a rather volatile solvent mixture in which to work 2-ethylanthraquinone, Dawsey, Umhoefer and Muehlhausser in U. S. Patent 2,455,238 more recently suggested certain nonvolatile dibasic acid esters as possessing advantages over the less permanent materials of I. G. Farbenindustrie (U. S. 2,215,883). Using an ester as a single solvent, it was possible greatly to reduce the cost of raw materials in making hydrogen peroxide. Oxygen gas was eliminated and replaced with comparatively cheap air. Evaporation losses of volatile materials, like benzene and hexyl alcohol, were eliminated. The accompanying explosion and fire hazards connected with working the volatile organic materials was eliminated giving a safe, simple and cheap process. Dibutyl sebacate was cited as an example of such a permanent type solvent. The disadvantage connected with these dibasic acid ester solvents, however, are that they lack chemical stability. The alkali wash required in the purification stage, through which the cycling work solution continuously passes,

I destroys part of the solvent; as a consequence, use of the dibasic acid esters is not as advantageous as a class of permanent solvents possessing the requisite chemical stability.

The present invention relates to improvements over the basic German process described in U. S. 2,158,525 U. S. 2,215,883, 2,537,516 and 2,537,655, wherein hydrogen peroxide is made by working a mixture containing two solvents. The novelty of the present invention resides in the discovery of a new class of quinone solvents. No claim is made herein in the improvement in the hydroquinone solvent component of the work solution since that has already been made the subject of other patents of Dawsey, Umhoefer and Muehlhausser (U. S. 2,537,516 and 2,537,655). This invention relates specifically to improvement in the quinone solvent component of the work solution, especially in compounding chemically stable, non-volatile and permanent work solutions which resist deterioration and loss over long periods of time.

It is an object of the invention to produce hydrogen peroxide from alkylated anthraquinones or the tetrahydro anthraquinones contained in a non-volatile organic work solution, wherein the oxidation step in the process may be carried out with air which is an extremely cheap raw material.

It is an object of the present invention to produce hydrogen peroxide from quinone type materials without the attendant explosion hazard heretofore present.

It is also an object of the invention to provide an improved solvent medium for such auto-oxidation process having great solvent power for the quinone constituent and as an ancillary object to improve the amount of hydrogen peroxide produced per operating cycle.

In accordance with the present invention, We have discovered that naphthalene and certain hydrocarbon derivatives of naphthalene possess both remarkable permanence and high solvent action on quinones. These substances exhibit little or no solvency for the corresponding hydroquinones however, so it is evident that they must be blended with another solvent having high specific solubility for the hydroquinone in order to give an operable work solution. This new class of quinone solvents consists of naphthalene, which is the parent compound, and certain alkyl hydrocarbon derivatives of naphthalene com pletely saturated with regard to structure with exception.

.of the naphthalene nucleus itself. The hydrocarbon deri at ve als m y in lude c rtain .a y .sub i-t to t naphthalene nucleus, such as for example, phe-nyl naphthalene, in which case the substituent group may be unsaturated in the aryl side grouping itself. Typical examples of some of the compounds falling within the genenal classification, all having from to carbon atoms, are as follows: naphthalene, methylnaphthalene, dimethylnaphthalene, ethyl-naphthalene, amyl-naphthalene, diamyl-n-aphthalene, phenyl-naphthalene and benzyl-naphthalene. As a class, these hydrocarbons have molecular weight ranging from 128 to 268 with boiling points ranging between 218 and 370 C. All have vapor pressures below 1 mm. Hg at room temperature, many have practically zero vapor pressure. Specific gravities may range between 0.930 and 1.180, depending upon the types of substitution on the naphthalene double ring. The viscosities of the liquid members at C. may range between 2 and 90 centipoises, although liquids with viscosities in the lower part of such range, for instance below 10 centipoises, are preferred. These quino-ne "solvents may be solids as well as liquids, when in the pure state, provided such solids remain dissolved when compounded with the other components used in making up the work solution, i. e. a solvent for the hydroquinone form (see Examples 1 and 3).

All members of the class are substantially and mutually insoluble with water, but are readily miscible with most organic solvents. Since they 'are not esters but hydrocarbons, they :are not afiected by water or dilute acids or strong lalkalis under ordinary conditions. However, they can be sulfonated :o-r nitrat-ed with the corresponding concentrated acids. They are chemically stable toward oxygen and peroxides under the conditions encountered in the anthraquinone autoaoxidation process for making hydrogen peroxide.

Solvents within the naphthalene hydrocarbon class have exceptional dissolving power for the alkylated anthraquinones as well as the corresponding tetrahydro alkylated anthraquinones. The following table lists the properties of five typical commercially available solvents together with the solubility of Z-ethylanthraquinone in each:

quinone; Z-ethyltetrahydroanthraquinone is about fourfifths as soluble as 2-ethylanthraquinone. As higher yields of peroxide per liter of solution throughput are obtained from solution of greatest alkyl anthraquinone concentration, the solubility of the alkyl anthraquinone dictates the choice of the particular alkyl anthraquinone to be inconporated in the working solution.

Although naphthalene and hydrocarbon naphthalene derivatives containing from 10 to 20 carbon atoms, with molecular weights in the range between 128 and 268, are quite suitable for use as a quinone form solvent, a solvent compound containing not more than 16 carbon atoms is the preferred solvent since solubility decreases with the size and number of substituent groups added to the naphthalene nucleus.

It is of course evident from the foregoing that mixtures of different naphthalenes are both suit-able and workable. Commercial dimethylnaphthalene, a by-product from coal tar distillation, is a mixture of l,4-dimethylnaphthalene which is a liquid of melting point 18 C., and 2,3- dimethylnaphthalene which is a solid of melting point 104 C. This is the solvent utilized in Example 3 below. A compound like alphamethyh, or betamethyl-naphthalene, having high solvency for the anthraquinones may be blended with an inert organic diluent to produce a mixture having a high quinone solvency. Also mixtures of petroleum products such as those produced through the so-called aromatizing cracking of hydrocarbon oils" which contain naphthalene *and isomers of methyl-, dimethyl-, trimethyland polymethyl-naphthalenes, distilling in the range between 240 C. and 300 C. are applicable after purification, according to this invention.

The following experimental examples illustrate the successful working of solutions employing the naphthalene hydrocarbon solvents. In considering these illustrations, it must be remembered that the hydroquinone solvent component, that is the phosphate or alcohol, has a limited dissolving power for the quinone and any quinone which may be worked is largely due to the dissolving power of the naphthalenes. Further, the examples are merely illustrative of the principles of the invention and are not to be deemed limitative thereof, as other alkylated anthra- TABLE I Quinone Solu- Solidifi- Boiling Spec. Viscosi- Flash bility, g./L.

cation Range, Gravity, ty, Gen- Point, Solvent point, C. 25 C. tipoise, F.

Naphthalene 1 80 218 980 187 276 500 Alphamethylnaphthalene -22 240-5 1. 014 2. 6 220 286 560 Dimethylnaphthalene 2 15 200-5 .995 3. l 245 268 490 Amylnaphthalene 3 230-330 960 7. 7 255 108 212 Diamylnaphthalene 3 30 330-66 930 89. 0 315 60 103 1 Specific gravity and quinone solubility calculated for naphthalene in solution.

bower members of the series have a dissolving power for the quinones equal to or superior to that of benzene which is known to dissolve 230 grams of Z-ethylan-thraquinone at 20 C., or 400 grams at 30 C., per liter.

The naphthalene hydrocarbons are eminently applicable in working of 2-ethylanthraquinone, 2-isopropyl anthraquinone or Z-tertiarybutylanthraquinone, in the auto-oxidation process for making hydrogen peroxide and are suitable for use with other alkyl substituted anthraquinones. Thus the solubility of Z-methylanthraquinone, in the naphthalene hydrocarbons is about A that of the Z-ethyl compound. On the other hand, 2-isopropylanthraquinone and 2-tert.-butylanthraquinone are considerably more soluble than the 2-ethylanthraquinone. In the case of the tetrahydro derivatives of the anthraquinones, tetrahydroanthraquinone and 2 methyltetrahydroanthraquinone are about one-half as soluble as 2-ethylanthraquinones may be employed in lieu of Z-ethylanthr-aquinone specifically illustrated as the working compound, and other naphthalene derivatives may be used in admixtures with or in lieu of that specifically illustrated.

Example I .Naphthalene 2000 cc. of this solution was hydrogenated at 36 C. with 9 grams of porous nickel catalyst in a spherical, 3-liter, glass reaction vessel which was equipped with a 1-inch diameter turbine agitator driven at 2000 R. P. M. During a period of 446 minutes, 19.2 liters of hydrogen gas was absorbed, measured at 25 C. and 750 mm. of Hg pressure, which was the calculated amount required to reduce 60% of the quinone present into the hydroquinone. The agitator was stopped, the reduced solution and catalyst were drained out of the hydrogenating vessel through a cock sealed in the bottom of the vessel, thence through a medium porosity, 90 mm. diameter, sintered glass filter where the catalyst was retained and into a 3-liter glass oxidizing vessel which was held under nitrogen atmosphere, and which was an exact duplicate of the hydrogenating vessel with regard to its construction. The nitrogen in the oxidation vessel was flushed out with air, after raising the temperature in the vessel to 36 C. and the reduced solution was oxidized at 36 C. with agitator running at 2000 R. P. M. Oxygen absorbed from the air atmosphere within the oxidizer was constantly replaced with pure, metered oxygen gas. After 160 minutes, oxygen absorption ceased abruptly with a change in color of the solution to yellow. The quantity of oxygen consumed was 17.35 liters, measured at 25 C. and 750 mm. Hg pressure. The hydrogen peroxide dissolved in the solution was extracted by washing five successive times with 200 cc. portions of water. The hydrogen peroxide recovered was 23.7 grams. The volume of work solution treated in the oxidizer was then measured and found to be 1985 cc. According to these figures, the oxygen consumption should have been 19.1 liters, whereas the actual uptake was 17.35 liters. This corresponds to a 9% loss of hydrogen which is assumed to have gone toward the formation of ethyltetrahydroanthraquinone during hydrogenation. Of the total oxygen used, 99.7% was recovered in the form of hydrogen peroxide. The overall efiiciency of hydrogen gas into hydrogen peroxide was 91%. According to this example, the concentration of hydrogen peroxide produced before extraction amounted to 11.9 grams per liter of work solution; that is, over twice the concentration (5.5 grams per liter) possible according to the earlier practice referred to herein, where benzene and alcohols were employed in solution make-up. This marked increase in the hydrogen peroxide production capacity is due in part to a simple substitution of naphthalene in place of the heretofore used benzene, in solution make-up.

The high flash point of this solution places it well out of the range of hazardous work materials. With an operating temperature of 36 C. in the oxidation vessel, working of this solution with flash point of 143 C. involved no risk of accidental ignition of vapors within the vessel. In comparison, however, the benzene-alcohol work solutions cited in the prior art have flash points of about C. The fire point is within the range of the actual operating temperature. Explosions with loss of life have been recorded in the past where benzene was employed as a solvent in the production. of hydrogen peroxide by the anthraquinone process.

The next example illustrates the practice of the inven tion wherein a naphthalene hydrocarbon is compounded with a higher alcohol, in place of a phosphate hydroquinone solvent.

Example II.-Methylnaphthalene Two liters of commercial alphamethylnaphthalene, initially red in color, was purified in a 3-1iter separatory funnel, by repeated shaking with 100 cc. portions of 85% sulfuric acid until the acid layer drawn off was nearly colorless. The temperature during the acid treatment was not allowed above 35 C. The tested solvent after filtration through a layer of 100-mesh activated alumina was practically colorless and of specific gravity 1.014 at 25 C.

A solvent mixture was made up consisting of 1000 cc. of the purified alphamethylnaphthalene and 1000 cc. of commercial tetradecanol, to give a 2000 cc. volume having a specific gravity of 0.925. In this mixture, 268 grams of 2-ethylanthraquinone was dissolved to give a work solution of 2218 cc. volume, with a specific gravity of 0.955 and a quinone concentration of 121 grams per liter. The work solution containing the quinone was then further purified by shaking with aqueous 50% KOH, in a separatory funnel, followed by filtration through a layer of activated alumina. It was then treated with an aqueous 40% KzCOa solution followed by another filtration to remove the aqueous cloud caused by this carbonate treatment. The final solution had a viscosity of 5.2 centipoise, at 25 C. and a flash point of C. in air. The solution was just saturated with regard to the quinone when it was held at a temperature of 19 C.

1940 cc. of the purified and conditioned solution was hydrogenated in the same apparatus and under the same conditions as described in Example I, with the exception that 6.0 grams of catalyst was used to cause the absorption of 9.22 liters of hydrogen during a 157-minute period. The absorbed hydrogen was the quantity required to reduce 37% of the quinone present to the hydroquinone. 1920 cc. of the reduced solution was filtered into the oxidation vessel and likewise oxidized as in Example I, with the consumption of 8.53 liters of oxygen during a period of 57 minutes. The work solution was extracted with water, as before, yielding 11.6 grams of hydrogen peroxide. According to these figures, the oxygen absorption should have been 9.12 liters, whereas the actual uptake was 8.53 liters. This corresponds to a 6% hydrogen loss which is assumed to have gone toward the formation of ethyltetrahydroanthraquinone during hydrogenation. Of the total oxygen used, 99% was recovered as hydrogen peroxide. The overall efiiciency of hydrogen gas into hydrogen peroxide was 93%.

The concentration of hydrogen peroxide produced in the work solution, before extraction, amounted to 6.1 grams per liter which is about the same as that possible with the benzene-alcohol work solutions of the prior art. However, the high flash point shown by the work solution in this example places it well within the class of safe media under actual oxidizing conditions, as contrasted with the low flash point characteristic of the benzene-alcohol work solutions cited in the prior art, which classifies the latter as a hazardous work medium.

Example Ill.-Dimethylnaphthalene A commercial mixture of dimethylnaphthalene isomers, originally reddish-brown in color, distilling between 260 and 265 C. were kept and purified in a 3-liter separatory funnel, as in the case of the alpha-methylnaphthalene cited in Example II. The purified sample was then practicaily colorless and of specific gravity 0.995. On chilling in ice, crystals of 2,3-dimethylnaphthalene separated from this solvent but redissolved at room temperature.

A solvent mixture was made up consisting of 667 cc. of the purified dimethylnaphthalene and 1333 cc. of commercial diphenylcresylphosphate to give a 2000 cc. volume having a specific gravity of 1.137. In this mixture, 320 grams of Z-ethylanthraquinone was dissolved to give a work solution of 2260 cc. volume of specific gravity 1.146 and a quinone concentration of 141 grams per liter. The flash point tested 151 C. The viscosity was 17 centipoise at 25 C. On continued standing, the quinone separated provided the temperature was held below 17 C.

The solution was treated with 40% potassium carbonate, as in Example I. 1740 cc. was hydrogenated in the same apparatus and under the same conditions as described in Example I, with the exception that 11 grams of catalyst was used to cause the absorption of 13.9 liters of hydrogen during a 234-minute period. The hydrogen absorbed corresponded to a reduction of 54% of the quinone present to the hydroquinone. 1720 cc. of the reduced solution was filtered into the oxidation vessel and oxidized under air, as in Example I, with the consumption of 12.7 liters of oxygen during a 116-minute period. The work solution was extracted with water, as before, yielding 17.25 grams of hydrogen peroxide. According to these figures, the oxygen absorption should have been 13.7 liters, whereas the actual uptake was 12.7 liters. This corresponds to a 7% hydrogen loss which is assumed tohave gone toward the formation of ethyltetrahydroanthraquinone during the hydrogenation. Of the total oxygen used, 99% was extracted as hydrogen peroxide. The overall efticiency of hydrogen into hydrogen peroxide was 92%.

The concentration of hydrogen peroxide in the work solution before extraction was 10 grams per liter, representing an 82% gain in work capacity .of this solution over a similar work solution compounded with the hitherto used benzene as quinone solvent. The high flash point exhibited by this solution places it in a safe category.

Example IV.-Amylnaphthalene A commercial mixture of monoamylnaphthalene isomers, originally reddish-yellow in color, distilling between 280 and 330 C. was purified with 98% sulfuric acid as in Example H, followed by filtration through a layer of activated alumina. It was then light yellow in color with a specific gravity of 0.960.

A solvent mixture was made up consisting of 1400 cc. of purified amyinaphthalene and 600 cc. of commercial trioctylphosphate to give a 2000 cc. volume having a specific gravity of 0.950. in this mixture was dissolved first, 148 grams of Z-ethyIanthraquinc-ne, then 82 grams of 2-ethyltetrahydroanthraquinone to give a work solution of 2186 cc. volume of specific gravity 0.974. The concentration of the first quinone was 67.5 grams per liter; that of the second quinone was 37.5 grams per liter, giving a total rnixed quinone concentration of 105 grams per liter of work solution. The dissolving point for the anthraquinone compound in this solution was 24 C., while that of the tetrahydroanthraquinone compound was below this temperature. The viscosity was 11.9 centipoise at 25 C. The flash point in air tested 152 C. by the open cup method. The solution was further purified with KOH and then with 40% KzCOa, as explained for the solution in Example II.

2000 cc. was hydrogenated in the same apparatus and underthe same conditions as described in Example I with the exception that 12.80 liters of hydrogen was absorbed in an 81-minute period with 6 grams of catalyst. The absorbed hydrogen corresponded to a 57.6% reduction of the total quinones present into the hydroquinones. 1970 cc. of the reduced solution was filtered into the oxidizer and oxidized under air as in Example I, with the consumption of 12.45 liters of oxygen during a 182-minute period. Upon extraction, the work solution yielded 16.7 grams of hydrogen peroxide. According to these figures, the oxygen absorption corresponded to 99% of the hydrogen absorption; therefore, little or no anthraquinone was further converted to tetrahydroquinone in the hydrogenation of this solution. Of the total ox gen used, 93% was recovered as hydrogen peroxide. The overall efficiency from hydrogen to hydrogen peroxide was 97%.

The concentration of hydrogen peroxide in the work solution before extraction was 8.5 grams per liter, representing a gain in work capacity of this solution over a similar work solution compounded with the hitherto used benzene and alcohol solvents.

The high flash point exhibited by this solution, together with its very low volatility mark it as an outstanding working medium for use in the continuous cyclic production of hydrogen peroxide.

Example V.Amylnaphthalene 38 liters of the solution described in Example IV, where the solvent consisted of amylnaphthalene and trioctylphosphate in the volume ratioof 7 to 3 and the concentration ratio of the anthraquinone to the tetrahydroanthraquinone was about 2 to 1, were prepared. This work solution was placed in a recycling system fitted with a pump capable of causing a continuous fiow around the system very much in the same fashion as the water pump in an automobile engine cooling system. In this case, however, the oil was caused to circulate from the pump through a system of vessels connected in series, consisting of hydrogenator, oxidizer, extractor, carbonate washer, alumina absorber, precontactor and then back to the pump whence the cycle was then repeated. The system contained 27.5 liters of the work solution which fiowed at the rate of 5 liters per hour giving a cycle period of 5.5 hours.

During continuous operation, hydrogen and nickel catalyst were added in the hydrogenation vessel, air was blown through the oxidizer (porous plate aeration) and distilled water was fed to the extractor. The concentration of peroxide produced in the oil during oxidation was 8.5 grams per liter, whereas the recovered peroxide from the extractor amounted to 40 grams per hour and was of 27.5% strength by weight. The catalyst yield amounted to about 270 grams of hydrogen peroxide per gram of nickel consumed in the hydrogenator. The overall practical efliciency of converting hydrogen gas into recovered hydrogen peroxide was about 87%.

The solution was so worked during a 20-month test period, both continuously and intermittently, until it had completed 600 cycles of operation. Although some of the oil was lost due to mechanical leaks from the systom, the specific gravity and the dissolving point for the anthraquinone compound in the solution remained substantially unchanged throughout the test period, indicating no degradation of the Working compound nor volatilization of the naphthalene solvents, all in spite of the fact the solution had been subjected to continuous aeration with large volumes of air during the 20-month test period.

From the foregoing it will be seen that the present invention provides a new class of quinone solvents of great permanence and of practical value in the manufacture of hydrogen peroxide according to the anthraquinone autooxidation process.

What is claimed is:

1. In the process for making hydrogen peroxide by reduction and auto-oxidation of a working material selected from the qroup of quinones consisting of the alkylated anthraquinones and of their tetrahydro derivatives dissolved in a 2-component solvent mixture consisting of a quinone solvent and a hydroquinone solvent, the improvement which comprises employing an alkyl naphthalene as a constituent of the solvent mixture for dissolving the quinone form of the working material.

2. In the process for making hydrogen peroxide by reduction and auto-oxidation of a working material selected from the group of quinones consisting of the alkylated anthraquinones and of their tetrahydro derivatives dissolved in a 2-component solvent mixture consisting of a quinone solvent and a hydroquinone solvent, the improvement which comprises employing a methyl naphthalene as a constituent of the solvent mixture for dissolving the quinone form of the working material.

3. In the process for making hydrogen peroxide by reduction and auto-oxidation of a working material selected from the qroup of quinones consisting of the alkylated anthraquinones and of their tetrahydro derivatives dissolved in a 2-component solvent mixture consisting of a quinone solvent and a hydroquinone solvent, the improvement which comprises employing a dimethyl naph- 9 thalene as a constituent of the solvent mixture for dissolving the quinone form of the working material.

4. In the process for making hydrogen peroxide by reduction and auto-oxidation of a working material selected from the qroup of quinones consisting of the alkylated anthraquinones and of their tetrahydro derivatives dissolved in a 2-component solvent mixture consisting of a quinone solvent and a hydroquinone solvent, the improvement which comprises employing a polymethyl naphthalene as a constituent of the solvent mixture for dissolving the quinone form of the working material.

5. In the process for making hydrogen peroxide by reduction and auto-oxidation of a working material selected from the qroup of quinones consisting of the alkylated anthraquinones and of their tetrahydro derivatives dissolved in a 2-component solvent mixture consisting of a quinone solvent and a hydroquinone solvent, the improvement which comprises employing an amyl naphthalene as a constituent of the solvent mixture for dissolving the quinone form of the working material.

6. In the process for making hydrogen peroxide by reduction and auto-oxidation of a working material selected from the qroup of quinones consisting of the alkyl- 10 ated anthraquinones and of their tetrahydro derivatives dissolved in a 2-component solvent mixture consisting of a quinone solvent and a hydroquinone solvent, the improvement which comprises employing a mixture of alkyl naphthalenes for dissolving the quinone form of the working material.

References Cited in the file of this patent UNITED STATES PATENTS 2,059,569 Filson Nov. 3, 1936 2,144,341 Michalek et a1 Jan. 17, 1939 2,158,525 Riedl et al. May 16, 1939 2,178,640 Michalek et al. Nov. 7, 1939 2,215,883 Riedl et al. Sept. 24, 1940 2,455,238 Dawsey et al. Nov. 30, 1948 2,537,516 Dawsey et al. Jan. 9, 1951 2,537,655 Dawsey et al. Ian. 9, 1951 2,668,753 Harris et al. Feb. 9, 1954 OTHER REFERENCES Solvents in Synthetic Organic Chemistry; MacArdle; copyright 1925 by D. Van Nostrand Co., pp. 127-128. 

1. IN THE PROCESS FOR MAKING HYDROGEN PEROXIDE BY REDUCTION AND AUTO-OXIDATION OF A WORKING MATERIAL SELECTED FROM THE GROUP OF QUINONES CONSISTING OF THE ALKYLATED ANTHRAQUINONES AND OF THEIR TETRAHYDRO DERIVATIVES DISSOLVED IN A 2-COMPONENT SOLVENT MIXTURE CONSISTING OF A QUINONE SOLVENT AND A HYDROQUINONE SOLVENT, THE IMPROVEMENT WHICH COMPRISES EMPLOYING AN ALKYL NAPHTHALENE AS A CONSTITUENT OF THE SOLVENT MIXTURE FOR DISSOLVING THE QUINONE FORM OF THE WORKING MATERIAL. 